Rake receiver for spread spectrum signal demodulation

ABSTRACT

The architecture of the present invention is premised upon an algorithm involving integration of oblique correlators and RAKE filtering to null interference from other spread spectrum signals. The oblique correlator is based on the non-orthogonal projections that are optimum for nulling structured signals such as spread spectrum signals. In one configuration, space spanned by a first signal associated with a first emitter is orthogonal to an interference space associated with one or more signals of one or more other emitters. RAKE filtering is used to rapidly steer the beam of the multi-antenna system and to mitigate the effects of multipath.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. PatentApplication entitled “Rake Receiver For Spread Spectrum SignalDemodulation”, having Ser. No. 09/612,602, filed Jul. 7, 2000 now U.S.Pat. No. 6,430,216, which is a continuation of U.S. Patent Applicationentitled “Rake Receiver For Spread Spectrum Signal Demodulation”, havingSer. No. 08/916,884, filed Aug. 22, 1997 now abandoned, which claimspriority under 35 U.S.C. §119(e) from U.S. Provisional Applicationentitled “PHASED-RAKE RECEIVER FOR SIGNAL DEMODULATION”, having Ser. No.60/024,525 and filed Aug. 23, 1996, and is a continuation-in-part ofU.S. patent application entitled “Method and Apparatus for AcquiringWide-Band Pseudorandom Noise Encoded Waveforms” having Ser. No.09/137,383, filed Aug. 20, 1998 now U.S. Pat. No. 6,252,535, whichclaims priority under 35 U.S.C. §119(e) from U.S. ProvisionalApplications entitled “Method and Apparatus for Acquiring Wide-BandPseudorandom Noise Encoded Waveforms” having Ser. No. 60/056,455 filedAug. 21, 1997, and entitled “Adaptive Digital Receiver” having Ser. No.60/056,228, filed Aug. 21, 1997, and entitled “Adaptive DigitalReceiver” having Ser. No. 60/087,036, filed May 28, 1998, and claimspriority under 35 U.S.C.§119(e) from U.S. Provisional Application Ser.No. 60/245,792, filed Nov. 3, 2000, all of which are incorporated fullyherein by reference.

FIELD OF THE INVENTION

The present invention is generally directed to a system for receiving aspread spectrum signal and specifically to a system for receiving anddemodulating a spread spectrum signal.

BACKGROUND OF THE INVENTION

Spread spectrum techniques are finding larger roles in a variety ofapplications. In cellular telephony, spread spectrum based systems offerthe potential for increased efficiency in the use of bandwidth. Theresistance of spread spectrum methods to jamming make them ideallysuited for radar and Global Positioning System (GPS) applications. Forradar applications, spread spectrum signals have a lower probability ofbeing intercepted due to the noise-like appearance of spread spectrumwaveforms. In addition, it may be used to increase the pulse repetitionfrequency without sacrificing unambiguous range.

In spread spectrum radars, GPS, and cellular telephony applications(e.g., Code Division Multiple Access (CDMA)), each transmitted signal orpulse is assigned a time varying pseudo-random (PN) code that is used tospread each bit in the digital data stream (i.e., an interference code),such as a PN code (e.g., a long code) in CDMA applications. In CDMAapplications, this spreading causes the signal to occupy the entirespectral band allocated to the Multiple Access System (MAS). Thedifferent users in such a system are distinguished by uniqueinterference codes assigned to each. Accordingly, all userssimultaneously use all of the bandwidth all of the time and thus thereis efficient utilization of bandwidth resources. In addition, sincesignals are wide-band, the multipath delays can be estimated andcompensated for. Finally, by carefully constructing interference codes,base-stations can operate with limited interference from adjacent basestations and therefore operate with higher reuse factors (i.e., more ofthe available channels can be used).

In spread spectrum systems, all other spread spectrum signals contributeto background noise, or interference, relative to a selected spreadspectrum signal. Because each user (or radar pulse or GPS satellitesignal) uses a noise-like interference code to spread the bits in asignal, all the users contribute to the background noise. In CDMAsystems in particular, user generated background noise, while having aminimal effect on the forward link (base-to-mobile) (due to thesynchronized use of orthogonal Walsh Codes), has a significant effect onthe reverse link (mobile to base)(where the Walsh Codes are commonly notsynchronized and therefore nonorthogonal). The number of users abase-station can support is directly related to the gain of the antennaand inversely related to the interference. Gain is realized through theamplification of the signal from users that are in the main beam of theantenna, thereby increasing the detection probability in thedemodulator. Interference decreases the probability of detection for asignal from a given user. Although “code” filters are used to isolateselected users, filter leakage results in the leakage of signals ofother users into the signal of the selected user, thereby producinginterference. This leakage problem is particularly significant when theselected user is far away (and thus the user's signal is weak) and theinterfering user is nearby (and thus the interfering user's signal isstrong). This problem is known as the near-far problem.

There are numerous techniques for improving the signal-to-noise ratio ofspectrum signals where the noise in the signal is primarily a result ofinterference caused by other spread spectrum signals. These techniquesprimarily attempt to reduce or eliminate the interference by differentmechanisms.

In one technique, the interfering signals are reduced by switchingfrequency intervals assigned to users. This technique is useless for theintentional jamming scenario in which jammers track the transmitterfrequencies. Frequency switching is not an option for the CDMA standardfor cellular telephones. In that technology, all users use all of thefrequencies at all times. As a result there are no vacant frequencybands to switch to.

In another technique, the interfering signals are selectively nulled bybeam steering. Classical beam steering, however, does not provide,without additional improvements, the required angular resolution fordensely populated communications environments.

The above techniques are further hampered due to the fact that signalsrarely travel a straight line from the transmitter to the receiver. Infact, signals typically bounce off of buildings, trees, cars, etc., andarrive at the receiver from multiple directions. This situation isreferred to as the multipath effect from the multiple paths that thevarious reflections that a signal takes to arrive at the receiver.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a systemarchitecture for increasing the signal-to-noise ratio (SNR) of a spreadspectrum signal. Another objective is to provide a system architecturefor removing the interference from a spread spectrum signal,particularly the interference attributable to spread spectrum signalsgenerated by other sources. Yet another objective is to provide a systemarchitecture for removing the interference from a spread spectrum signalthat does not employ beam steering. Specific related objectives includeproviding a demodulating/decoding system for efficientlydemodulating/decoding spread spectrum signals generated by far awaysources in the presence of spread spectrum signals generated by nearsources and/or effectively accounting for the various multipaths of aspread spectrum signal.

These and other objectives are addressed by the spread spectrum systemarchitecture of the present invention. In one embodiment, the systemincludes: (i) an antenna adapted to receive a signal that isdecomposable into first and second signal segments, the first signalsegment of the signal being attributable to a first source and thesecond signal segment of the signal being attributable to a source otherthan the first source; and (ii) an oblique projecting device, incommunication with the antenna, for determining the first signalsegment. The signal can be any structured signal, such as a spreadspectrum signal, that is decomposable into at least a first signalsegment and a second signal segment. A “structured signal” is a signalthat has known values or is created as a combination of signals of knownvalues.

In one configuration, the oblique projecting device determines the firstsignal segment by obliquely projecting a signal space spanned by thesignal onto a first space spanned by the first signal segment. As usedherein, the “space” spanned by a set “A” of signals is the set of allsignals that can be created by linear combinations of the signals in theset “A”. For example, in spread spectrum applications, the space spannedby the signals in set “A” are defined by the interference codes of theone or more selected signals in the set. Thus the space spanned byinterfering signals is defined by all linear combinations of theinterfering signals. The signal space can be obliquely projected ontothe axis along a second space spanned by the second signal segment. Theestimated parameters of the first signal segment are related to theactual parameters of the first signal segment and are substantially freeof contributions by the second signal segment. Through the use ofoblique projection, there is little, if any, leakage of the secondsignal segment into computed parameters representative of the firstsignal segment.

For spread spectrum applications where noise characteristics arequantifiable, oblique projection is preferably performed utilizing thefollowing algorithm:(y^(T)(I-S(S^(T)S)⁻¹S^(T))H(H^(T)(I-S(S^(T)S)⁻¹S^(T))H)⁻¹H^(T)(I-S(S^(T)S)⁻¹S^(T))y)/σ²where y corresponds to a selected portion of the spread spectrum signal,H corresponds to an interference code matrix for the first signalsegment (which defines a first space including the first signal), Scorresponds to the interference code matrices for signals of all of theother sources (users) in the selected portion of the spread spectrumsignal (which defines a second space including the signals of the othersources), ^(T) corresponds to the transpose operation and σ² correspondsto the variance of the magnitude of the noise in the selected portion ofthe spread spectrum signal. Were noise is present, a substantial portionof the noise may be generated by the receiver. As will be appreciated,the oblique projection can be done using other suitable algorithms.

In another embodiment, a system for receiving a signal is provided thatincludes:

(a) one or more antennas adapted to receive a signal, the signal beingdecomposable into at least a first and a second CDMA signal segmentattributable to first and second emitters, respectively; and

(b) a projection filter for determining the first CDMA signal segment,the first CDMA signal segment spanning a first signal space, theprojection filter being in communication with the one or more antennasand determining the first CDMA signal segment by projecting a signalspace spanned by the signal onto the first signal space. The firstsignal space is orthogonal to an interference space that corresponds toan interference code matrix for the second CDMA signal segment and/orsecond emitter.

In one configuration, the system performs an oblique projection byobliquely projecting the signal space spanned by the signal onto thefirst signal space along the interference space.

The system can have a number of advantages, especially in spreadspectrum systems. The system can significantly increase thesignal-to-noise ratio (SNR) of the spread spectrum signal relative toconventional spread spectrum demodulating systems, thereby increasingthe detection probability. This is realized by the almost completeremoval (i.e., nulling) from the spread spectrum signal of interferenceattributable to spread spectrum signals generated by other sources.Non-orthogonal (oblique) projections are optimum for nulling structuredsignals such as spread spectrum signals. In CDMA systems, the system canefficiently demodulate/decode spread spectrum signals generated by faraway (weak) sources in the presence of spread spectrum signals generatedby near (strong) sources, thereby permitting the base station and/ormobile station for a given level of signal quality to service more usersand operate more efficiently. An improvement in SNR further translatesinto an increase in the user capacity of a spectral bandwidth—which is ascarce resource. Unlike conventional systems, the system does notrequire beam steering to remove the interference.

In applications where the first signal includes a number of multipathsignal segments, the system in one configuration includes a thresholddetecting device, in communication with the oblique projecting device,for generating timing information defining a temporal relationship amongthe plurality of multipath signal segments (e.g., using mathematicalpeak location techniques that find the points at which the slope of thesurface changes from positive to negative and has a large magnitude)and/or a timing reconciliation device for determining a reference timebased on the timing information (i.e., the multipath delays). Multipathsignal segments correspond to the various multipaths followed by asignal (e.g., the first signal) after transmission by the signal source.

In one configuration, the system includes a RAKE processor incommunication with the oblique projecting device and the timingreconciliation device for aligning the plurality of multipath signalsegments in at least one of time and phase and/or scaling themagnitude(s) of the multipath signal segments. RAKE processing rapidlysteers the beam of a multi-antenna system as well as mitigates multipatheffects. The RAKE processor preferably aligns and scales using thefollowing algorithm:${y_{R}(K)} = {\frac{1}{\sum\limits_{i = 1}^{P}\quad A_{i}}{\sum\limits_{i = 1}^{P}\quad{A_{i}{\mathbb{e}}^{- {j\varphi\mathbb{i}}}{y\left( {k + t_{i}} \right)}}}}$where p is the number of the multipath signal segments (or peaks); i isthe number of the multipath signal segment; A_(i) is the amplitude ofith multipath signal segment; j is the amount of the phase shift; φ_(i)is the phase of the ith multipath signal segment; y(k) is the inputsequence; and t_(i) is the delay in the received time for the ithmultipath signal segment.

In one configuration, the oblique projecting device nulls out thesignals of other sources in the spread spectrum signal and the RAKEprocessor then effectively focuses the beam on the desired signalsource. The process eliminates the need for null steering to beperformed by the antenna. The system of the present invention is lesscomplex and more efficient than conventional beam steering systems.

In one configuration, the system includes a demodulating device incommunication with the RAKE processor to demodulate each of the signalsegments. Like the oblique projecting device, the demodulating devicepreferably uses the equation noted above with respect to the obliqueprojecting device. Unlike the oblique projecting device which usesportions of the filtered signal to perform oblique projection, thedemodulating device uses the output of the RAKE processor which hasaligned and summed all of the multipath signal segments. Both theoblique projecting and demodulating devices use estimates of thetransmission time (“trial time”) and symbol (“candidate symbol”) and thereceive time in determining a correlation function using one or more ofthe above equations. “Receive time” is the index into the received datastream (or spread spectrum signal) and represents the time at which thedata (or spread spectrum signal) was received by the antenna.“Transmission time” is the time at which the source transmitted aselected portion of the data stream (i.e., the selected signal).

In one configuration, the system includes a plurality of antennas (i.e.,an antenna array), with each antenna having a respective obliqueprojecting device, threshold detecting device, and RAKE processor. Inone configuration, a common timing reconciliation device is incommunication with each of the respective threshold detecting devicesand RAKE processors. In one configuration, a common demodulatingcomponent is also in communication with each of the RAKE processors. Inthis configuration, the demodulating component sums all of the firstsignals received by each of the antennas to yield a corrected firstsignal reflecting all of the various multipath signal segments relatedto the first signal.

In these configurations, the system can effectively accommodate thevarious multipath signal segments related to a source signal. The RAKEprocessor weights each of the multipath signal segments in directrelation to the magnitude of the peak defined by each multipath signalsegment.(y^(T)(I-S(S^(T)S)⁻¹S^(T))H(H^(T)(I-S(S^(T)S)⁻¹S^(T))H)⁻¹H^(T)(I-S(S^(T)S)⁻¹S^(T))y)/σ²

The above description of the configurations of the present invention isneither complete nor exhaustive. As will be appreciated, otherconfigurations are possible using one or more of the features set forthabove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first embodiment of the present invention;

FIG. 2 depicts the various components of the correlating device;

FIG. 3 depicts the unit steps performed by the components of FIG. 2;

FIG. 4 depicts graphically the oblique projecting operation;

FIG. 5 depicts the signal segments contained in a portion of thefiltered signal;

FIG. 6 depicts the three dimensional correlation surface output by thebank of projection filters in the correlating device of FIG 1;

FIG. 7 pictorially depicts the operation of the RAKE processor;

FIG. 8 depicts the various components of the demodulating device;

FIG. 9 depicts a correlation surface defined by the correlation functionoutput by the bank of projection filters in the demodulating device ofthe FIG. 1;

FIG. 10 is a second embodiment of the present invention for an antennaarray;

FIG. 11 is the first part of a flow schematic of the software foroperating the system of FIG. 10; and

FIG. 12 is the second part of the flow schematic.

DETAILED DESCRIPTION

The present invention provides a software architecture and theunderlying mathematical algorithms for demodulating/decodingcommunications signals containing interference noise. This invention isgenerally applicable to CDMA systems (and other spread spectrumsystems), Frequency Division Multiple Access systems (FDMA) and TimeDivision Multiple Access systems (TDMA) and particularly for spreadspectrum systems, such as CDMA. In spread spectrum systems, interferencenoise is typically due to a dense population of signals using the sameintervals of the frequency spectrum, such as in high user densitycellular phone applications, or such as in the intentional interferenceof radar or communication signals by nearby jammers.

Single Antenna Systems

An overview of the current architecture for detecting signals from anith user in a CDMA system is illustrated in FIG. 1. The architectureemploys a single antenna for receiving CDMA signals. The system includesthe antenna 50 adapted to receive the spread spectrum signal andgenerate an output signal 54, filters 58 and 60 for filtering thein-phase (“I”) and quadrature (“Q”) channels to form filtered channelsignals 62 and 66, a correlating device 70 for providing a hypotheticalcorrelation function characterizing a filtered signal segment, which maybe multipath signal segment(s) of a source signal (hereinaftercollectively referred to as a “signal segment”), transmitted by aselected user, a first threshold detecting device 74 for generatingtiming information defining the temporal relationship among a pluralityof peaks defined by the hypothetical correlation function, a timingreconciliation device 78 for determining a reference time based on thetiming information, a RAKE processor 82 for aligning multipath signalsegments for each selected user in time and phase and outputting analigned signal for the selected user, a demodulating device 86 fordemodulating aligned signals transmitted by each selected user intocorrelation functions and, finally, a second threshold detecting device90 for converting the correlation functions into digital information. Aswill be appreciated, a system configured for radar or GPS applicationsmay not include some of these components, such as the filters 58 and 60,and the conversion from analog to digital may be performed either at REor IF.

The antenna can be of any suitable configuration for receiving astructured signal and providing the output signal based thereon, such asan antenna having one or a number of antenna elements. As will beappreciated, the output signal is a mix of a plurality of signalsegments transmitted by a number of mobile units (or users). The outputsignal is coherently shifted down from radio frequency and split into anin-phase (I) channel and a quadrature (Q) channel.

The I and Q channels of the output signal are filtered by the filters,H*(f), designated as 58 and 60, to form the filtered signals 62 and 66.Filtered signal 62 corresponds to the I channel of the output signalwhile filtered signal 66 corresponds to the Q channel. The filters 58and 60 are counterparts to the filter H(f) applied at the mobile unit tocontain the transmitted signal within the specified bandwidth.

Referring to FIGS. 1-3, the correlating device 70 includes a user codegenerator 94, a projection builder 98, and a bank of projection filters102. For each of the filtered signals 62 and 66, the user code generator94 selects 106 a user (i.e., the selected user) transmitting a selectedsignal segment in a selected portion of the filtered signal to bedecoded, selects 110, for the selected user and signal segment, a set oftrial transmit times (“trial times”) and/or candidate symbols and, foreach trial time and/or candidate symbol in the set, generates 114 acandidate user code (or interface code) for the selected user and signalsegment. As will be appreciated, a candidate symbol is typically notrequired in GPS applications and in a CDMA forward link. In selectingtrial times, the base-station is assumed to have approximatesynchronization with each of the mobile units. Using this approximatesynchronization, the base station has a set of trial times at which eachselected mobile unit may have transmitted the selected signal segmentincluded in the filtered signals 62 and 66. For each trial time, t_(p),in the set of trial times for the selected user and signal segment, theuser code generator 94 generates one or more candidate user codesindexed by trial time and candidate symbol. The set of trial times usedby the user code generator for determining the set of candidate usercodes for a given signal segment is determined by known techniques.Typically, the user code generator will use a time interval centered onthe receive time for the signal segment that has a width of about 200milliseconds or less and more typically of about 50 milliseconds orless. These steps are repeated for each of the active users transmittingsignal segment(s) of the filtered signal.

The projection builder 98 selects 118 a portion of the filtered signalto process, collects 122 appropriate candidate user codes for the userstransmitting signal segments of the selected filtered signal portionfrom the output of the user code generator, and, using the receive timeoffsets, trial times, and candidate symbols, creates 126 a set ofhypothetical projection operators.

The hypothetical projection operators are generated using the algorithm:(I-S(S^(T)S)⁻¹S^(T))H(H^(T)(I-S(S^(T)S)⁻¹S^(T))H)⁻¹H^(T)(I-S(S^(T)S)⁻¹S^(T))where H corresponds to an interference code matrix for the selectedsignal segment, S corresponds to the interference code matrices for allof the other signal segments in the selected filtered signal portion, Iis the identity matrix, and ^(T) corresponds to the transpose operation.The variables H and S depend upon the interference codes determined bythe user code generator 94. Accordingly, H and S depend, respectively,upon the transmit time for the selected signal segment, and the transmittimes of all of the other signal segments in the selected filteredsignal portion. Because the data is indexed by the receive time, S isalso a function of the receive time.

To apply the above-equation, the projection builder 98 estimates thetransmit times and/or symbols of each of the signal segments in theselected filtered signal portion. As noted, the trial time is anestimate of the transmit time and/or the candidate symbol of the symbol.

Next, the bank of projection filters 102, with one filter correspondingto each trial time and/or candidate symbol (i.e., to each hypotheticalprojection operator), provide a set of filter outputs (i.e.,hypothetical correlation functions) to be threshold detected by thefirst threshold detecting device 74. Each of the bank of projectionfilters correlates 130 a plurality of multipath signal segments for agiven trial time and/or candidate symbol. The projection filters 102extract an estimated signal segment attributable to a given user fromeach selected filtered signal portion while simultaneously nulling outthe other signal segments from other users.

For each data segment y that is processed, the matrix S is assembledfrom the interfering codes. The time, code, phase and Doppler offsetsare estimated as in current receivers. These offsets ensure that thecorrect interference code segment is used to build S.

The equation used to generate the various hypothetical correlationfunctions is:(y^(T))(projection operator for selected signal portion)(y)/σ²where y corresponds to the selected filtered signal portion 62 or 66 andσ² corresponds to the variance of the magnitude of the noise portioncontained in the respective filtered signal portion. The equation isbased on oblique or non-orthogonal projections of y onto space spannedby H to null interference (i.e., interference from signal segmentstransmitted by other users) and yield the signal segment transmitted bythe selected user. Because the receive times for the various signalsegments of a selected user are unknown, a number of signal segments ofthe user, each at a different receive-time offset, must be correlated bythe bank of projection filters.

The oblique projection of Y space 134 spanned by y onto H space 138spanned by H to yield an estimate of the signal segment 142 issimplistically illustrated in FIG. 4. Y space 134 spanned by Y isobliquely projected onto the H space 138 along S space 146 spanned by S.The test to determine whether H space is present in measurement y isdetermined by extending signal segment 142 into the space P_(s) ^(⊥) 148to yield signal segment 149. P_(s) ^(⊥)space refers to the space that isorthogonal to the space that is spanned by the columns of matrix S. Anillustrative discussion of this approach applied to the detection ofsubspace signals in subspace interference and broadband noise iscontained in Scharf, et al., “Matched Subspace Detectors,” pages 2146 to2157, Vol. 42, No. 8 IEEE. Transactions on signal processing, August1994, which is fully incorporated herein by this reference. As will beappreciated S space 146 is normal or perpendicular to P_(s) ^(⊥)space148; Y space 134 is obliquely directed relative to (i.e., is notorthogonal relative to) S space 146, H space 138, and P_(s) ^(⊥)space148; the dashed line 147 represents space that is parallel to H space;the dashed line 145 represents space that is parallel to S space 146;and angle θ is oblique. (e.g., is not 90° but is an acute or obtuseangle). As will be appreciated, Y space, H space, S space and P_(s)^(⊥)are each N-dimensional space. Oblique projections are more effectivethan orthogonal projections in removing interference attributable to theother users where the spread spectrum codes are not synchronized andthus not orthogonal, such as in the case of Walsh codes in the reverselink of a CDMA system. In such cases, the correlation function isindependent of the amplitudes of the signal segments of other users and,therefore, power control of the transmitter is not a significantconsideration. By way of illustration, FIG. 5 illustrates a four (4)user system in which the various users are transmitting symbolsrepresenting bits of data. The source signals are received by theantenna 50 as a number of multipath signal segments. A first multipathsignal segment 150 is transmitted by a first user, a second multipathsignal segment 154 by a second user, a third multipath signal segment158 by a third user, a fourth multipath signal segment 162 by the firstuser, and a fifth multipath signal segment 166 from a fourth user. Theprojection builder 98 selects a first receive time offset Δt₁ andthereby selects the first, second and third multipath signal segments150, 154 and 158. The value of the receive time offset is determined bythe control or receiver signal tracking system for the base stationusing known techniques. For the first multipath signal segment 150, theprojection builder 98 employs Δt₁ and a trial time and/or candidatesymbol in the projection operator equation and generates a hypotheticalprojection operator for the first user indexed by the trial time andcandidate symbol. For the second multipath signal segment 154, theprojection builder employs Δt₁ and a trial time and/or candidate symbolin the projection operator equation and generates a hypotheticalprojection operator for second user indexed by the trial time andcandidate symbol. This operation may also be performed for the thirdmultipath signal segment 158 with a hypothetical projection operator forthe third user being likewise generated. For the second receive timeoffset, Δt₂, the projection builder repeats the above steps for each ofthe fourth and fifth multipath signal segments 162 and 166 to generateadditional projection operators for the first and fourth users. Althoughthe first and fourth multipath signals are multipaths of a common sourcesignal, the hypothetical projection operators for the first and fourthmultipath signal segments are different due to differing degrees ofinterference. These steps are repeated for subsequent receive timeoffsets. The number of receive time offsets generated is determined bythe base station control or receiver signal tracking system using knowntechniques. The bank of projection filters 102 then apply each of thehypothetical projection operators to the filtered signal portioncorresponding to the respective receive time offset to develop aplurality of hypothetical correlation functions for the various users.Each of the hypothetical correlation functions defines a correlationsurface 170 of the type depicted in FIG. 6, where the horizontal axesrepresent receive time and trial time and the vertical axis representsthe output of the correlation function for a specific pair of receivetimes and trial times. One correlation function corresponds to a sourcesignal transmitted by the selected user. Each peak 174 a-d represents amultipath signal segment of the source signal.

The first threshold detecting device 74 uses the hypotheticalcorrelation functions for each user that are outputted by the bank ofprojection filters 102 to determine the temporal locations of thevarious multipath signal segments in the hypothetical correlationfunction. Due to multipath delays, each hypothetical correlationfunction can have multiple peaks as shown in FIG. 6. As set forth above,the various peaks in the correlation surface can be isolated using knownmathematical techniques. Using techniques known in the art and thetemporal location of the peaks (or timing information) output by thefirst threshold detecting device 74, the timing reconciliation device 78determines a reference time for the RAKE processor 82. The referencetime is based upon the receive times of the various peaks located by thefirst threshold detecting device 74. The reference time is used by theRAKE processor 82 as the time to which all of the signal segments for agiven user are aligned.

The RAKE processor 82 based on the timing information, the peakamplitudes of the hypothetical correlation function(s) detected by thefirst threshold detecting device, and the filtered signals 62 and 66scales and aligns (in time and phase) the various multipath signalsegments transmitted by a given user and then sums the aligned signalsegments for that user. The RAKE processor 82 can be a maximal SNRcombiner.

The operation of the RAKE processor is illustrated in FIG. 7 (for anantenna array). As noted, the output of the bank of projection filtersis the hypothetical correlation function, which in multipathenvironments typically has multiple peaks. Assuming that there are pmultipaths or signal segments and therefore p peaks, the RAKE processdetermines the amplitudes, {A_(i)}^(P) _(j=1), time delays, {t_(i)}^(P)_(i=1), and phase delays {Ø_(i)}^(P) _(i=1). If y(k) is a sequencedefining the filtered signal 62 or 66, then the “RAKED” sequence isy_(R)(K):${y_{R}(K)} = {\frac{1}{\sum\limits_{i = 1}^{P}\quad A_{i}}{\sum\limits_{i = 1}^{P}\quad{A_{i}{\mathbb{e}}^{- {j\varphi\mathbb{i}}}{y\left( {k + t_{i}} \right)}}}}$Referring again to FIGS. 1 and 7 (which illustrates the operation ofRAKE processor 82), the RAKE processor 82 first sums 178 the outputs ofthe various antenna elements, shifts 182 the various sequences in theoutputs by the amounts of the multipath delays between the correspondingmultipath signal segments of a selected signal segment, so that allmultipath signal segments are perfectly aligned. It then weights eachshifted multipath signal segment by the amplitude of the correlationfunction corresponding to that segment and sums 186 the weightedcomponents to produce the aligned signal y_(R)(k). The aligned signaly_(R)(k) is then detected 187 to form digital output 188.

The demodulating device 86 correlates the “RAKED” sequence, y_(R)(k)with the appropriate replicated segment of the coded signal in thefilter bank 102 to produce the correct correlation function fordetection by a second threshold detecting device 90. Referring to FIGS.1 and 8 (which illustrates the components of demodulating device 86),the demodulating device 86, like the correlating device 70 includes auser code generator 200, a projection builder 204, and a bank ofprojection filters 208. The projection builder 204 and bank ofprojection filters 208 use the equations set forth above to provideprojection operators and correlation functions. Unlike the correlatingdevice 70 which provides for a series of hypothetical projectionoperators and correlation functions based on the trial time, receivetime, and candidate symbol for each multipath signal segment, thedemodulating device 86 uses the “RAKED” sequence which has only a singlealigned signal segment rather than a plurality of independent multipathsignal segments. Accordingly, the demodulating device 86 is able toreliably estimate the actual transmit time for the source signal andtherefore requires considerably less processing to determine acorrelation function than the correlating device 70.

For each of the I and Q channels, the user code generator 200 in thedemodulating device 86 selects the user to decode for each alignedsignal segment, selects a transmit time and symbol for the alignedsignal segment and, for each transmit time and symbol, generates theuser or interference code for the selected user.

The projection builder 204 selects a portion of the “RAKED” sequence toprocess, collects the pertinent user codes from the user code generator200, and, using the receive times, transmit times, and symbols, createsa series of projection operators for each aligned signal segment in the“RAKED” sequence.

Next, the bank of projection filters 208, with one filter correspondingto each pair of transmit times and symbols and therefore each projectionoperator, provides a set of filter outputs (e.g., correlation functions)each defining a second correlation surface to be threshold detected.

The second correlation surface is then detected by a second thresholddetecting device 90 to determine the actual transmit time and symbol foreach aligned signal. FIG. 9 depicts a representative correlation surface212 corresponding to a correlation function determined by one projectionfilter. Compared to the correlation surface 170 of FIG. 6, thecorrelation surface 212 has only a single peak 214 (due to the alignmentof the multipath signal segments in the “RAKED” sequence) as opposed tomultiple peaks.

Using the transmit time and symbol, the aligned signal segment can bedespread to provide the digital data for the aligned signal segmenttransmitted by each user.

Because the above-described system assumes that the interference fromother users is substantially the same for all multipath signal segmentsand/or that the amount of the interference in each multipath signalsegment is relatively small, the RAKE processor 82 and demodulatingdevice 86 require reconfiguration in applications where the interferencein each of the multipath signal segments is substantially different andthe interference is significant. To accommodate the differinginterference portions in each multipath signal segment, the user codegenerator 200, projection builder 204, and bank of projection filters208 process each multipath signal segment, corresponding to a peak inthe correlation surface, before the RAKE processor has aligned, scaled,and summed each of the multipath signal segments. After the interferenceportion of each multipath signal segment is removed by obliqueprojection techniques from that signal segment, the various multipathsignal segments can be aligned, scaled, and summed by the RAKE processoras set forth above. Alignment and scaling can be performed after obliqueprojection is completed as to a given multipath signal segment or afterall oblique projection is completed for all multipath signal segments.

Multiple Antenna Systems

FIG. 10 depicts a multiple antenna system according to anotherembodiment of the present invention. Each antenna 50 a-n is connected tofilters 250 a-n and 254 a-n, correlating device 258 a-n, thresholddetecting device 262 a-n, and a RAKE processor 266 a-n. The thresholddetecting devices 262 a-n for all of the antennas 50 a-n are connectedto a common timing reconciliation device 270, which in turn is connectedto all of the RAKE processors 266 a-n. In this manner, all of the RAKEprocessing for all of the filtered signals is performed relative to acommon reference time. The combined output of the RAKE processors 266a-n is provided to a common demodulating device 274 for determination ofthe correlation functions and summing of the signal portions received byall of the antennas that are attributable to a selected user. The systemin effect “phases” the output of each antenna in order to maximize theSNR.

As will be appreciated, the output of each antenna in a conventionalantenna array contains a desired signal but at a delay relative to theoutputs of the other antennas. The amount of relative delay is afunction of the arrangement of the antennas as well as the angularlocation of the source. Conventional beam-steering methods attempt tocompensate for this time delay so that the desired signals addconstructively thereby increasing the power of the desired signal. Ingeneral, an N antenna system can improve the SNR by a factor of N.

In the multiple antenna system of the present invention, by contrast,the compensation for the relative delays is performed in the RAKEprocessors 266 a-n. In order to accomplish this, the system sums theantenna outputs without compensating for the relative delays. Thecorrelation process may result in Np peaks as opposed to just pmultipath induced peaks. These Np peaks are then used to align and scalethe various signal segments prior to summation. The RAKE processor, ineffect, performs the phase-delay compensation usually done inbeam-steering.

The system architecture of the present invention thus does not requireknowledge of array geometries and steering vectors. It does not requireiterative searches for directions as is the case for systems that steerthe beam using techniques like LMS and its variants. Finally, it iscomputationally very efficient.

Referring to FIGS. 11-12, the software to operate the multiple antennasystem of FIG. 10 will now be described. The software detects spreadspectrum signals in the presence of interference from other users.

Initially, a channel is opened 278 to the respective antenna 50 a-n, anda user is selected 282 to demodulate the signal segments transmitted bythe selected user. The outputted spread spectrum signal of therespective antenna 50 a-n is converted 286 into the I and Q channels.The channels are filtered by the filters 250 a-n and 254 a-n to form thefiltered signals 290 a-n and 294 a-n. As will be appreciated, thefiltering operation is generally not performed in radar and GPSapplications.

For each data segment y that is processed, the matrix S is assembledfrom the interfering codes. The time, code, phase and Doppler offsetsare estimated as in current receivers. These offsets ensure that thecorrect interference code segment is used to builds.

Filtered signal portions are selected 298 for processing. In the querybox 302, if other users are present in the selected filtered signalportion, P^(⊥) _(s) is set 306 based on candidate interference codes. Ifnot, P^(⊥) _(s) is set 310 to I.

After the user is selected in box 282, trial times are generated 314 forthe selected user. Next, candidate user codes are generated 318 for eachof the trial times.

Next, hypothetical projection operators are created 322 for each trialtime and filtered signal portion to be processed. The filtered signalportion is correlated 326 by user with the trial time, receive time, andcandidate symbol to create the hypothetical correlation function. Thehypothetical correlation function characterizes the multipath signalsegments from the user of interest while nulling out the interferencefrom other known users.

A correlation surface is generated and thresholded 330 to identify peaksin the hypothetical correlation functions.

Based on the receive times for all multipath signal segments for a givensource signal received by each of the antennas, timing reconciliation334 is performed. The minimum receive time of all of the correspondingmultipath signal segments is selected as the reference time.

Based on the magnitudes of the peaks and the estimated receive times andthe reference time, RAKE processing 338 is performed on all of the datasegments.

The outputs from of the RAKE processors 266 a-n are combined 342 to forma combined output 343.

Using the correct user codes and the correct interference codes, whichare provided by RAKE processing, projection operators are created 346for each data segment.

Based on the projection operators and the combined output, the alignedmultipath signals segments for all of the antennas are correlated 350and a second correlation surface generated.

Threshold detection 354 is performed to provide the digital data. Theabove-noted steps are repeated for other users and/or other multipathsignal segments.

Location Using Multiple Antenna System

The multiple antenna system of FIG. 10 can be utilized to locate thesource of a selected signal by triangulation. In case the multipleantennas on a base-station are evenly$\theta = {\sin^{- 1}\left( \frac{{ct}_{0}}{d} \right)}$spaced, with spacing d, then the time difference between when the firstsignal from the source impinges on any two antennas can be used toestimate direction of arrival of the signal. This approach assumes thatthe first signal is a direct signal from the source. If θ is the angleto the source and to is the time delay from when the first signal hitsthe first antenna and then the second antenna, then the formula forcomputing θ is:whered-antenna spacing

c-speed of light

Using ranging protocols currently in base-stations, one can obtainestimates of range to the source. This range information either alone orin combination with angle estimates, when obtained from multiplebase-stations, can be processed using decentralized filtering algorithmsto get accurate location information about the source. The decentralizedfiltering algorithms are known. Examples of decentralized filteringalgorithms include decentralized Kalman filters and the Federatedfilter.

While various embodiments of the present invention have been describedin detail, it is apparent that modifications and adaptations of thoseembodiments will occur to those skilled in the art. However, it is to beexpressly understood that such modifications and adaptations are withinthe scope of the present invention, as set forth in the followingclaims.

1. A system for receiving a signal, comprising: an antenna adapted toreceive a signal, the signal being decomposable into first and secondCDMA signal segments attributable to first and second emitters,respectively; and projecting means for determining the first CDMA signalsegment, the first CDMA signal segment spanning a first signal space,the projecting means being in communication with the antenna anddetermining the first CDMA signal segment by projecting a signal spacespanned by the signal onto the first signal space, wherein the firstsignal space is orthogonal to a space that corresponds to aninterference code matrix for the second CDMA signal segment.
 2. Thesystem of claim 1, wherein the signal space is obliquely projected ontothe first signal space along a second signal space spanned by the secondCDMA signal segment.
 3. The system of claim 1, wherein the systemincludes: a) a plurality of antennas, each of which receives at least aportion of the signal, and b) a plurality of projecting meanscorresponding with the plurality of antennas and being in communicationtherewith, each of the plurality of projecting means being adapted todetermine by projection the first CDMA signal segment of the respectivesignal portion received by the corresponding antenna.
 4. The system ofclaim 3, further comprising a plurality of RAKE processors correspondingwith the plurality of projecting means, wherein each of the plurality ofprojecting means produces a respective projecting means output which isreceived as a RAKE processor input by a RAKE processor corresponding toeach of the plurality of projecting means, the respective output of eachof the plurality of projecting means being delayed relative to oneanother, each of the plurality of RAKE processors being adapted to alignand scale its respective input to produce a compensated output.
 5. Thesystem of claim 4, wherein the compensated output of each of theplurality of RAKE processors is delivered to a summing correlator. 6.The system of claim 1, further including a RAKE processor having a RAKEinput, wherein the projecting means produces a projecting means outputwhich is coupled to the RAKE input.
 7. The system of claim 1, whereinthe first CDMA signal segment comprises a plurality of multipath signalsegments and the projecting means outputs a correlation function havinga plurality of peaks corresponding to the plurality of multipath signalsegments, and further comprising: threshold detecting means, incommunication with the projecting means, for generating timinginformation defining a temporal relationship among the plurality ofpeaks.
 8. The system of claim 7, wherein the system comprises aplurality of projecting means and a plurality of antennas incommunication with a corresponding threshold detecting means and furthercomprising: timing reconciliation means for determining a reference timebased on timing information received from each of the thresholddetecting means.
 9. The system of claim 8, further comprising: a RAKEprocessing means, in communication with each of the projecting means andthe timing reconciliation means, for aligning the plurality of multipathsignal segments in at least one of time and phase as a function of atleast one of the magnitudes of the plurality of multipath signalsegments, the reference time, and the phase, the RAKE processing meansoutputting an aligned first signal.
 10. The system of claim 9, furthercomprising: a plurality of RAKE processing means, each RAKE processingmeans being in communication with a corresponding one of the pluralityof antennas and producing a corresponding aligned first signalattributable to the first emitter; and a demodulating means, incommunication with the plurality of RAKE processing means, fordemodulating at least a portion of each corresponding aligned firstsignal, the at least a portion of each corresponding aligned firstsignal defining a respective aligned first space, the demodulating meansdetermining the respective corresponding aligned first signals byobliquely projecting a respective signal space defined by acorresponding aligned first signal onto the respective aligned firstspace.
 11. A system for receiving a signal, comprising: an antennaadapted to receive a signal and adapted to generate an output signal,the output signal being decomposable into: (i) a first CDMA signalportion attributable to a first source, and (ii) at least one secondCDMA signal portion, the at least one second CDMA signal portion beingattributable to at least one second source; and, a projection filter incommunication with the antenna for determining the first CDMA signalportion of the output signal, the projection filter being incommunication with the antenna and determining the first CDMA signalportion of the output signal by projecting a signal space spanned by theoutput signal onto a first signal space that corresponds to the firstCDMA signal portion, wherein the first signal space is orthogonal to aninterference space that corresponds to one or more interference codematrixes corresponding to the at least one second CDMA signal portion.12. The system of claim 11, wherein the output signal includes a noiseportion and the antenna includes a receiver and at least a portion ofthe noise portion is generated by the receiver.
 13. The system of claim12, further comprising a projection builder operable to determine aprojection operator corresponding to the first CDMA signal portion bythe following equation:(y^(T)(I-S(S^(T)S)⁻¹S^(T))H(H^(T)(I-S(S^(T)S)⁻¹S^(T))H)⁻¹H^(T)(I-S(S^(T)S)⁻¹S^(T))y)/σ²wherein y corresponds to the output signal, H is related to aninterference code matrix of the first source, S is related to aninterference code matrix of at least a second source, ^(T) the transposeoperation, I denotes the identity matrix, and σ² corresponds to thevariance of the magnitude of the noise portion.
 14. The system of claim12, further including a plurality of projection filters corresponding toa plurality of antennas and being in communication therewith, each ofthe plurality of projection filters being adapted to determine arespective first CDMA signal portion of a corresponding portion of thesignal received by each of the plurality of antennas and determine therespective first CDMA signal portion of the signal using the equation ofclaim
 13. 15. The system of claim 14, further including a plurality ofRAKE processors in communication with a corresponding one of theplurality of projection filters, wherein each of the plurality ofprojection filters produces a corresponding projection filter outputwhich is received as a RAKE processor input by its corresponding RAKEprocessor, the corresponding projection filter output of each of theplurality of projection filters being delayed relative to one another,each of the plurality of RAKE processors being adapted to align andscale their respective inputs to produce a corresponding compensatedoutput.
 16. The system of claim 15, wherein the correspondingcompensated output of each of the plurality of RAKE processors isdelivered to a second projection filter in communication therewith fordetermining a refined first CDMA signal portion of each of thecompensated outputs.
 17. The system of claim 12, wherein the first CDMAsignal portion comprises a plurality of multipath signal segments andthe projection filter outputs a correlation function having a pluralityof peaks corresponding to the plurality of multipath signal segments,and further comprising: a threshold detector, in communication with theprojection filter, for generating timing information defining a temporalrelationship among the plurality of peaks.
 18. The system of claim 17,wherein the system comprises a plurality of antennas in communicationwith a corresponding threshold detector and further comprising: a timingreconciliation device for determining a reference time based on timinginformation received from each of the threshold detectors.
 19. Thesystem of claim 18, further comprising: one or more RAKE processors, incommunication with the projection filters and the timing reconciliationdevice, for aligning the plurality of multipath signal segments in atleast one of time and phase based on the magnitudes of the plurality ofmultipath signal segments and the reference time to form an alignedfirst CDMA signal.
 20. A method for processing a composite signal, themethod comprising the steps of: (a) providing a composite signal that isdecomposable into a first CDMA signal portion that is attributable to afirst emitter and at least one second CDMA signal that is attributableto a second emitter; and (b) obliquely projecting a signal spacecorresponding to the composite signal onto a first signal spacecorresponding to the first CDMA signal portion to determine a parameterof the first CDMA signal portion, wherein the first signal space isorthogonal to an interference space that corresponds to an interferencecode matrix corresponding to the second emitter.
 21. The method of claim20, wherein the signal space is obliquely projected onto the firstsignal space along a space that is at least substantially parallel tothe interference space.
 22. The method of claim 20, wherein theprojecting step determines the magnitude of the first CDMA signalportion and wherein the first and second CDMA signal portions aretransmitted asynchronously.
 23. The method of claim 20, wherein thefirst CDMA signal portion comprises a plurality of multipath signalsegments and further comprising: aligning at least one of a receivedtime and phase of the multipath signal segments to produce an alignedfirst signal.
 24. The method of claim 23, further comprising: scalingthe multipath signal segments.
 25. The method of claim 20, wherein thefirst CDMA signal portion comprises a plurality of multipath signalsegments, each of the plurality of multipath signal segments beingreceived at different times, and further comprising: assigning to aportion of each of the plurality of multipath signal segments arespective time of receipt.
 26. The method of claim 25, furthercomprising: determining a reference time of receipt based on therespective times of receipt.
 27. The method of claim 25, furthercomprising: correlating the plurality of multipath signal segmentswithout regard to the differing times of receipt to form a summated peakmagnitude; aligning the plurality of multipath signal segments relativeto the reference time of receipt to form a plurality of aligned signals;scaling each of the multipath signal segments to form a plurality ofscaled signals; and summing the scaled signals.
 28. The method of claim22, further comprising: determining an actual time of transmission ofthe first CDMA signal portion; determining an actual received time forthe first CDMA signal portion; and repeating step (b) using an actualtime of transmission of the first CDMA signal portion and the actualreceived time.
 29. The method of claim 20, further comprising the stepof generating at least one projection operator according to theequation:(y^(T)(I-S(S^(T)S)⁻¹S^(T))H(H^(T)(I-S(S^(T)S)⁻¹S^(T))H)⁻¹H^(T)(I-S(S^(T)S)⁻¹S^(T))y)/σ²where y corresponds to the composite signal, H is related to aninterference code matrix of the first emitter, S is related to aninterference code matrix of at least a second emitter, ^(T) denotes thetranspose operation, I denotes the identity matrix and σ² corresponds tothe variance of the magnitude of a noise portion of the compositesignal.
 30. A method for decomposing a composite signal having first andsecond CDMA signal segments attributable to first and second emitters,respectively comprising: projecting a signal space spanned by thecomposite signal onto a first signal space spanned by the first CDMAsignal segment to determine a parameter of the first CDMA signalsegment, wherein the first signal space is orthogonal to an interferencespace that corresponds to an interference code matrix associated withthe second CDMA signal segment; and processing the parameter.
 31. Themethod of claim 30, wherein, in the projecting step, the signal space isobliquely projected onto the first signal space along the interferencespace.
 32. The method of claim 30, wherein the composite signal includesa second CDMA signal segment attributable to a second emitter other thanthe first emitter and wherein the first and second CDMA signal segmentsare transmitted asynchronously.
 33. The method of claim 30, wherein thefirst CDMA signal segment comprises a plurality of multipath signalsegments and further comprising: aligning at least one of a receivedtime and phase of the multipath signal segments to produce an alignedfirst signal.
 34. The method of claim 33, further comprising: scalingthe multipath signal segments.
 35. The method of claim 33, wherein thefirst CDMA signal segment comprises a plurality of multipath signalsegments, each of the plurality of multipath signal segments beingreceived at different times, and further comprising: assigning to aportion of each of the plurality of multipath signal segments arespective time of receipt.
 36. The method of claim 35, furthercomprising: determining a reference time of receipt based on therespective times of receipt.
 37. The method of claim 35, furthercomprising: correlating the plurality of multipath signal segmentswithout regard to the differing times of receipt to form a summated peakmagnitude; aligning the plurality of multipath signal segments relativeto the reference time of receipt to form a plurality of aligned signals;scaling each of the multipath signal segments to form a plurality ofscaled signals; and summing the scaled signals.
 38. The method of claim30, further comprising: determining an actual time of transmission ofthe first CDMA signal segment; determining an actual received time forthe first CDMA signal segment; and repeating step (b) using an actualtime of transmission of the first CDMA signal segment and the actualreceived time.
 39. The method of claim 30, further comprising the stepof generating a plurality of projection operators according to theequation:(y^(T)(I-S(S^(T)S)⁻¹S^(T))H(H^(T)(I-S(S^(T)S)⁻¹S^(T))H)⁻¹H^(T)(I-S(S^(T)S)⁻¹S^(T))y)/σ²where y corresponds to the composite signal, H is related to aninterference code matrix of the first emitter, S is related to aninterference code matrix of at least a second emitter, ^(T) denotes thetranspose operation, I denotes the identity matrix and σ² corresponds tothe variance of, the magnitude of a noise portion of the compositesignal.
 40. A system for processing an output signal of an antenna, theoutput signal corresponding to a composite signal, comprising: at leastone projection filter for determining a parameter of an oblique CDMAprojection of the output signal of the antenna, the oblique CDMAprojection being attributable to an emitter having an interference codematrix and the at least one projection filter determining a parameter ofthe oblique CDMA projection by projecting obliquely a signal spacespanned by the output signal onto a signal space spanned by the obliqueCDMA projection and wherein an interference space corresponds to aninterference code matrix corresponding to a second CDMA signal segmentin the composite signal and the interference space is orthogonal to CDMAsignal space spanned by the oblique CDMA projection.
 41. The system ofclaim 40, wherein the antenna includes a receiver and at least a portionof a noise portion of the output signal is generated by the receiver.42. The system of claim 40, further comprising a plurality of projectionbuilders corresponding to a plurality of antennas and being incommunication therewith, each of the plurality of projection buildersbeing adapted to determine a respective oblique CDMA projection of acorresponding portion of a respective composite signal received by eachof the plurality of antennas and determine the respective oblique CDMAprojection of the corresponding output signal by the equation:(y^(T)(I-S(S^(T)S)⁻¹S^(T))H(H^(T)(I-S(S^(T)S)⁻¹S^(T))H)⁻¹H^(T)(I-S(S^(T)S)⁻¹S^(T))y)/σ²where y corresponds to the output signal, H is related to aninterference code matrix of the emitter, S is related to an interferencecode matrix of at least a second emitter, ^(T) denotes the transposeoperation, I denotes the identity matrix, and σ² corresponds to thevariance of the magnitude of a noise portion of the output signal. 43.The system of claim 42, wherein the at least one projection filtercomprises a plurality of projection filters corresponding to theplurality of antennas and further comprising a plurality of RAKEprocessors in communication with a corresponding one of the plurality ofprojection filters, wherein each of the plurality of projection filtersproduces a corresponding projection filter output which is received as aRAKE processor input by each of the plurality of projection filter'scorresponding RAKE processor, the corresponding projection filter outputof each of the plurality of projection filters being delayed relative toone another, each of the plurality of RAKE processors being adapted toalign and scale their respective inputs to produce a correspondingcompensated output.
 44. The system of claim 43, wherein thecorresponding compensated output of each of the plurality of RAKEprocessors is delivered to a second projection filter in communicationtherewith for determining a refined projection filter of each of thecompensated outputs.
 45. The system of claim 40, wherein the obliqueCDMA projection comprises a plurality of multipath signal segments andthe projection filter outputs a correlation function having a pluralityof peaks corresponding to the plurality of multipath signal segments,and further comprising: a threshold detector, in communication with theprojection operator, for generating timing information defining atemporal relationship among the plurality of peaks.
 46. The system ofclaim 45, wherein the system comprises a plurality of antennas incommunication with a corresponding threshold detector and furthercomprising: a timing reconciliation device for determining a referencetime based on timing information received from each of the thresholddetectors.
 47. The system of claim 46, further comprising: one or moreRAKE processors, in communication with the projection filters and thetiming reconciliation device, for aligning the plurality of multipathsignal segments in at least one of time and phase based on themagnitudes of the plurality of multipath signal segments and thereference time to form an aligned first signal.
 48. A system forprocessing an output signal of an antenna, the output signalcorresponding to a composite signal and being decomposable into a firstoblique projection attributable to a first source having an interferencecode matrix, comprising: projecting means for obliquely projecting asignal space spanned by the output signal onto a first signal spacespanned by the first CDMA oblique projection to determine a parameter ofthe first oblique projection wherein an interference space correspondsto an interference code matrix affiliated with a second CDMA signalsegment in the composite signal and the interference space is orthogonalto first signal space spanned by the first signal space.
 49. The systemof claim 48, wherein the composite signal is decomposable into thesecond signal segment, the second signal segment being attributable to asecond source other than the first source and wherein the signal spaceis obliquely projected onto the first signal space along a second signalspace corresponding to the second signal segment.
 50. The system ofclaim 49, wherein the system includes: a) a plurality of antennas, eachof which receives at least a portion of the composite signal, and b) aplurality of projecting means corresponding with the plurality ofantennas and being in communication therewith, each of the plurality ofprojecting means being adapted to determine by oblique projection thefirst oblique projection of the respective output signal received by thecorresponding antenna.
 51. The system of claim 50, including a pluralityof RAKE processors corresponding with the plurality of projecting means,wherein each of the plurality of projecting means produces a respectiveprojecting means output which is received as a RAKE processor input byeach of the plurality of projecting means' corresponding RAKE processor,the respective output of each of the plurality of projecting means beingdelayed relative to one another, each of the plurality of RAKEprocessors being adapted to align and scale its respective input toproduce a compensated output.
 52. The system of claim 51, wherein thecompensated output of each of the plurality of RAKE processors isdelivered to a summing correlator.
 53. The system of claim 48, furtherincluding a RAKE processor having a RAKE input, wherein the projectingmeans produces a projecting means output which is coupled to the RAKEinput.
 54. The system of claim 48, wherein the first oblique projectioncomprises a plurality of multipath signal segments and the projectingmeans outputs a correlation function having a plurality of peakscorresponding to the plurality of multipath signal segments, and furthercomprising: threshold detecting means, in communication with theprojecting means, for generating timing information defining a temporalrelationship among the plurality of peaks.
 55. The system of claim 54,wherein the system comprises a plurality of projecting means and aplurality of antennas in communication with a corresponding thresholddetecting means and further comprising: timing reconciliation means fordetermining a reference time based on timing information received fromeach of the threshold detecting means.
 56. The system of claim 55,further comprising: a RAKE processing means, in communication with eachof the projecting means and the timing reconciliation means, foraligning the plurality of multipath signal segments in at least one oftime and phase as a function of at least one of the magnitudes of theplurality of multipath signal segments, the reference time, and thephase, the phased RAKE means outputting an aligned first signal.
 57. Thesystem of claim 56, further comprising: a plurality of RAKE processingmeans, each RAKE processing means being in communication with acorresponding one of the plurality of antennas and producing acorresponding aligned first signal; and a demodulating means, incommunication with the plurality of RAKE processing means, fordemodulating at least a portion of each corresponding aligned firstsignal, the at least a portion of each corresponding aligned firstsignal defining a respective aligned first space, the demodulating meansdetermining the respective corresponding aligned first signals byobliquely projecting a respective signal space defined by acorresponding aligned first signal onto the respective aligned firstspace.
 58. A method for processing a composite CDMA signal, comprising:(a) estimating at least one of a time offset, a code offset, and aDoppler offset corresponding to at least one CDMA signal segment; (b)determining an interference code corresponding to the at least one CDMAsignal segment in response to (a); and (c) building a space S using theinterference code.
 59. The method of claim 58, wherein steps (a) and (b)are repeated for at least one other signal segment and in step (c) aplurality of interference codes are used to build S.
 60. The method ofclaim 58 further comprising: (d) estimating at least one of a timeoffset, a code offset, and a Doppler offset corresponding to a secondCDMA signal segment; (e) determining a second interference codecorresponding to the second CDMA a signal segment in response to (d);(f) building a space H using the second interference code; and (g)determining a projection operator using the S and H spaces.
 61. Themethod of claim 60, further comprising: (h) determining a correlationfunction using the projection operator.
 62. A system for processing acoded signal, comprising: an input for receiving a coded signal, thecoded signal being decomposable into a first signal segment and at leasta second signal segment, the first signal segment being attributable toa first emitter, and the at least a second signal segment beingattributable to at least a second emitter different from the firstemitter; and at least a first correlator operable to output at least afirst correlation function corresponding to the first signal segment ofthe coded signal, the first correlator being operable to project a codedsignal space spanned by the coded signal onto a first signal spacespanned by the first signal segment to determine a parameter associatedwith the first signal segment, wherein the first signal space isorthogonal to an interference space corresponding to at least oneinterference code matrix associated with the at least a second signalsegment.
 63. The system of claim 62, wherein the at least a firstcorrelator is operable to obliquely project the coded signal space ontothe first signal space.
 64. The system of claim 62, wherein the firstcorrelator comprises: at least a first projection builder operable tooutput a first set of projection operators.
 65. The system of claim 64,wherein the at least a first projection builder each projection operatorin the first set using the following mathematical expression:(I-S(S^(T)S)⁻¹S^(T))H(H^(T)(I-S(S^(T)S)⁻¹S^(T))H)⁻¹H^(T)(I-S(S^(T)S)⁻¹S^(T))where H is related to a first interference code matrix of the firstemitter, S is related to the at least one interference code matrix ofthe at least a second emitter, ^(T) denotes the transpose operation, andI denotes the identity matrix.
 66. The system of claim 64, wherein theat least a first correlator comprises: a user code generator operable tooutput for the first emitter a set of trial transmit times and candidatesymbols corresponding to the first signal segment and, for each pairingof trial transmit times and candidate symbols in the set, generate acandidate user code for the first emitter and wherein the at least afirst projection builder uses the candidate user codes to determine thefirst set of projection operators.
 67. The system of claim 66, whereinthe at least a first correlator comprises: a bank of projection filters,each projection filter in the bank of projection filters correspondingto each projection operator in the first set of projection operators,operable to output the at least a first correlation function.
 68. Thesystem of claim 67, wherein each of the projection filters is operableto output the at least a first correlation function attributable to thefirst emitter from the corresponding projection operator in the firstset of projection operators while simultaneously nulling outinterference attributable to emitters different from the first emitter.69. The system of claim 67, further comprising: a threshold detectoroperable to determine temporal locations of selected peaks in the atleast a first correlation function.
 70. The system of claim 69, furthercomprising: a timing reconciliation device operable to determine areference time based on the temporal locations of the selected peaks.71. The system of claim 70, wherein the at least a first correlationfunction comprises a plurality of correlation functions and furthercomprising: based on the reference time, a RAKE processor operable toalign in phase and time and then scale each of the plurality ofcorrelation functions to form a plurality of aligned and scaledcorrelation functions and sum the plurality of aligned and scaledcorrelation functions to form a RAKE output.
 72. The system of claim 71,further comprising: a demodulator operable to determine, based on theRAKE output, an actual transmit time for the first signal segment. 73.The system of claim 72, wherein the demodulator comprises: a second usercode generator operable to output for the first emitter a second set oftrial transmit times and candidate symbols corresponding to the firstsignal segment and, for each pairing of trial transmit times andcandidate symbols in the set, generate at least a second candidate usercode for the first emitter; a second projection builder to determine,for the at least a second candidate user code and based on the RAKEoutput, a second set of projection operators; and a second bank ofprojection filters, each filter being associated with a projectionoperator in the second set of projection operators, operable to outputat least a second correlation function.
 74. The system of claim 73,further comprising: a second threshold detector operable to determine anactual transmit time and symbol based on the at least a secondcorrelation function.
 75. The system of claim 74, further comprising: adecoder operable to despread the RAKE output using the actual transmittime and symbol.
 76. The system of claim 62, further comprising: atleast one antenna operable to receive the coded signal and at least oneoutput operable to output first and second channel signals correspondingto the coded signal.
 77. The system of claim 76, wherein the firstchannel signal corresponds to an in-phase portion of the coded signaland the second channel signal corresponds to a quadrature portion of thecoded signal.
 78. A method for processing a coded signal, comprising:providing a coded signal, the coded signal comprising a first signalsegment and at least a second signal segment; and projecting a codedsignal space spanned by the coded signal onto a first signal spacespanned by the first signal segment to determine a parameter associatedwith the first signal segment, wherein the first signal space isorthogonal to an interference space corresponding to at least oneinterference code matrix associated with the at least a second signalsegment.
 79. The method of claim 78, wherein in the projecting step thecoded signal space is obliquely projected onto the first signal space.80. The method of claim 78, wherein the output of the projecting step isat least a first correlation function corresponding to the first signalsegment.
 81. The method of claim 80, further comprising: generating afirst set of projection operators associated with the first signalsegment.
 82. The method of claim 81, wherein the generating step isperformed using the following mathematical expression:(I-S(S^(T)S)⁻¹S^(T))H(H^(T)(I-S(S^(T)S)⁻¹S^(T))H)⁻¹H^(T)(I-S(S^(T)S)⁻¹S^(T))where H is related to a first interference code matrix of the firstemitter, S is related to the at least one interference code matrix ofthe at least a second emitter, ^(T) the transpose operation, and Idenotes the identity matrix.
 83. The method of claim 81, furthercomprising: outputting for the first emitter a set of trial transmittimes and candidate symbols corresponding to the first signal segment;and for each pairing of trial transmit times and candidate symbols inthe set, generating a candidate user code for the first emitter andwherein the candidate user codes are used to generate the first set ofprojection operators.
 84. The method of claim 83, further comprising:detecting temporal locations of selected peaks in the at least a firstcorrelation function.
 85. The method of claim 84, further comprising:determining a reference time based on the temporal locations of theselected peaks.
 86. The method of claim 85, wherein the at least a firstcorrelation function comprises a plurality of correlation functions andfurther comprising: based on the reference time, aligning in phase andtime and then scaling each of the plurality of correlation functions toform a plurality of aligned and scaled correlation functions; andsumming the plurality of aligned and scaled correlation functions toform a RAKE output.
 87. The method of claim 86, further comprising:determining, based on the RAKE output, an actual transmit time for thefirst signal segment.
 88. The method of claim 87, further comprising:outputting for the first emitter a second set of trial transmit timesand candidate symbols corresponding to the first signal segment; and foreach pairing of trial transmit times and candidate symbols in the set,generating at least a second candidate user code for the first emitter.89. The method of claim 88, further comprising: determining, for the atleast a second candidate user code and based on the RAKE output, asecond set of projection operators; and based on the second set ofprojection operators, outputting at least a second correlation function.90. The method of claim 89, further comprising: determining an actualtransmit time and symbol based on the at least a second correlationfunction.
 91. The method of claim 90, further comprising: despreadingthe RAKE output using the actual transmit time and symbol.
 92. Themethod of claim 78, further comprising: converting the coded signal intofirst and second channel signals.
 93. The method of claim 92, whereinthe first channel signal corresponds to an in-phase portion of the codedsignal and the second channel signal corresponds to a quadrature portionof the coded signal.
 94. A system for processing a coded signal,comprising: an input for a coded signal, the coded signal beingdecomposable into a first signal segment and at least a second signalsegment; and at least a first projection filter operable to project acoded signal space spanned by the coded signal onto a first signal spacespanned by the first signal segment to determine a parameter of thefirst signal segment, wherein the first signal space is orthogonal to aninterference space corresponding to at least one interference codematrix associated with the at least a second signal segment.
 95. Thesystem of claim 94, wherein the at least a first projection filter isoperable to project obliquely the coded signal space onto the firstsignal space, the first signal segment being attributable to a firstemitter having a first interference code matrix.
 96. The system of claim95, wherein the at least a first projection filter outputs at least afirst correlation function corresponding to the first signal segment.97. The system of claim 96, further comprising: at least a firstprojection builder operable to output a first set of projectionoperators.
 98. The system of claim 97, wherein the at least a firstprojection builder generates each projection operator in the first setusing the following mathematical expression:(I-S(S^(T)S)⁻¹S^(T))H(H^(T)(I-S(S^(T)S)⁻¹S^(T))H)⁻¹H^(T)(I-S(S^(T)S)⁻¹S^(T))where H is related to the first interference code matrix of the firstemitter, S is related to the at least one interference code matrix of atleast a second emitter different from the first emitter and associatedwith the at least a second signal segment, ^(T) the transpose operation,and I denotes the identity matrix.
 99. The system of claim 97, furthercomprising: a user code generator operable to output for the firstemitter a set of trial transmit times and candidate symbolscorresponding to the first signal segment and, for each pairing of trialtransmit times and candidate symbols in the set, generate a candidateuser code for the first emitter and wherein the at least a firstprojection builder uses the candidate user codes to determine the firstset of projection operators.
 100. The system of claim 99, furthercomprising: a bank of projection filters, each projection filter in thebank of projection filters corresponding to each projection operator inthe first set of projection operators, operable to output the at least afirst correlation function.
 101. The system of claim 100, wherein eachof the projection filters is operable to output the at least a firstcorrelation function attributable to the first emitter from thecorresponding projection operator in the first set of projectionoperators while simultaneously nulling out interference attributable toemitters different from the first emitter.
 102. The system of claim 101,further comprising: a threshold detector operable to determine temporallocations of selected peaks in the at least a first correlationfunction.
 103. The system of claim 102, further comprising: a timingreconciliation device operable to determine a reference time based onthe temporal locations of the selected peaks.
 104. The system of claim103, wherein the at least a first correlation function comprises aplurality of correlation functions and further comprising: based on thereference time, a RAKE processor operable to align in phase and time andthen scale each of the plurality of correlation functions to form aplurality of aligned and scaled correlation functions and sum theplurality of aligned and scaled correlation functions to form a RAKEoutput.
 105. The system of claim 104, further comprising: a demodulatoroperable to determine, based on the RAKE output, an actual transmit timefor the first signal segment.
 106. The system of claim 105, wherein thedemodulator comprises: a second user code generator operable to outputfor the first emitter a second set of trial transmit times and candidatesymbols corresponding to the first signal segment and, for each pairingof trial transmit times and candidate symbols in the set, generate atleast a second candidate user code for the first emitter; a secondprojection builder to determine, for the at least a second candidateuser code and based on the RAKE output, a second set of projectionoperators; and a second bank of projection filters, each filter beingassociated with a projection operator in the second set of projectionoperators, operable to output at least a second correlation function.107. The system of claim 106, further comprising: a second thresholddetector operable to determine an actual transmit time and symbol basedon the at least a second correlation function.
 108. The system of claim107, further comprising: a decoder operable to despread the RAKE outputusing the actual transmit time and symbol.
 109. The system of claim 94,further comprising: at least one antenna operable to receive the codedsignal; and at least one output operable to output first and secondchannel signals corresponding to the coded signal.
 110. The system ofclaim 109, wherein the first channel signal corresponds to an in-phaseportion of the coded signal and the second channel signal corresponds toa quadrature portion of the coded signal.
 111. The system of claim 94,wherein the at least a first projection filter is a plurality ofprojection filters operable to project obliquely a respective codedsignal space corresponding to a respective coded signal onto arespective first signal space spanned by a respective first signalsegment of the respective coded signal.